In recent years, an electronic device or more specifically a portable electronic device has been needed to be improved in size, thickness and function. Therefore, it is necessary to enhance the density of electronic components to be mounted on a printed-circuit board of the portable electronic device, and to improve the portable electronic device in heat radiation performance.
As shown in FIGS. 13 to 15, the portable electronic device of this type is exemplified by a mobile phone. As shown in FIG. 13, the electronic device 100 includes a lower housing 103, an upper housing 105, and a hinge unit 104 for connecting the lower housing 17 with the upper housing 105 to allow opening and closing movements of the lower housing 17 and the upper housing 105. The lower housing 103 has an operation input unit 102 and a sound input unit 103 accommodated therein, while the upper housing 104 has a screen 106 and a sound output unit 107 accommodated therein.
The lower housing 101 has a front member 101a and a rear member 101b. As shown in FIG. 14, a printed-circuit board 121 for communications and input/output control, and a key sheet 122 having an elastic sheet section 122a retain key tops 122b, 122c, and 122d, and a flexible electrically-insulating sheet 123. When the key tops 122b, 122c, and 122d are operated, the press switches corresponding to the key tops 122b, 122c, and 122d selectively assume open and closed state (see FIG. 15).
More specifically, the flexible electrically-insulating sheet 123 has an area which corresponds to a key contact section 120, and has bores 125 as shown in FIG. 15. The flexible electrically-insulating sheet 123 includes a thermally-conductive sheet 123a constituted by a sheet made of electrically-nonconducting and thermally-conductive material, an electrically-conductive film 123b located on the opposite side of the thermally-conductive sheet 123a from the printed-circuit board 121, a resin sheet 123c located on the opposite side of the electrically-conductive film 123b from the thermally-conductive sheet 123a, and dome-shaped sections 124 constituted as switch elements corresponding to contact points 120 on the printed-circuit board 121, made of metal, and received in the bores 125 (see patent document 1). The above-mentioned press switch can diffuse heat loss from the electronic circuit 129 to avoid the temperature elevation of a surface for key operations on the side to be operated.
Patent document 1: Japanese Patent Laid-Open Publication 2006-310035